1. Field of the Invention
The present invention relates to a drive apparatus, a press machine slide drive apparatus and a method, and more particularly, to a drive apparatus, a press machine slide drive apparatus and a method using an electric motor and a hydraulic pump/motor such as oil hydraulic pump/motor together.
2. Description of the Related Art
There are conventional press machine slide drive apparatuses as shown below:
(a) An electric press that servo-drives the slide directly or indirectly (via a reduction gear, etc.) by an electric (servo) motor (only) (Japanese Patent No. 2506657).
(b) The press machine slide drive apparatus described in U.S. Pat. No. 4,563,889 drives the slide via a variable discharge capacity hydraulic pump, (a plurality of) hydraulic motors and screws.
(c) There is also a type of press machine slide drive apparatus that drives a machine press crank axis using a hydraulic circuit similar to above-described (b) (Japanese Patent Application Publication No. 1-309797, etc.). Furthermore, Japanese Patent Application Publication No. 1-309797 discloses the technology of providing a flywheel between an electric motor and variable capacity pump/motor and storing energy in this flywheel.
(d) A press machine slide drive apparatus which is provided with an electric motor that rotates and drives a fixed discharge capacity pump capable of discharging in both directions and is driven by a hydraulic cylinder and hydraulic motor connected to the pump (Japanese Patent Application Publication No. 10-166199).
The electric press in (a) described above can obtain a high degree of control over the slide, but cannot secure (provides insufficient) work performance (energy performance) which is an important performance element of a press machine or molding machine. This is because the electric press servo-driven by the electric servo motor does not have the function of storing energy and the amount of energy obtained from the motor during molding is limited.
Solving this problem requires provision of an electric motor with considerably high output (W), which in turn requires an enormous amount of the corresponding power reception capacity (facility) on the user side. Furthermore, during acceleration or deceleration or uniform motion not involving molding of the slide, the electric motor handles a small workload associated with extremely low load torque, and is therefore unable to use surplus torque (energy) effectively.
Moreover, the press machine slide drive apparatus in (b) described above has a problem with slide controllability (responsiveness and static (velocity and position) accuracy). That is, the force required to drive the slide is proportional to the pressure (load pressure) produced when the amount of oil flowing per unit time discharged by the variable discharge capacity pump is compressed in a conduit connected to the hydraulic motor caused by the load produced, and therefore the dynamic characteristic of the slide decreases due to a response delay caused by the compression (responsivity, velocity and position feedback gain decrease).
Furthermore, leakage of the hydraulic oil proportional to the load pressure is produced from the variable discharge capacity hydraulic pump, hydraulic motor and valves, which drastically reduces the velocity and positional accuracy especially during molding during which the load pressure increases. Moreover, since the slide is driven mainly under control over the amount of oil by the variable capacity pump motor, a large amount of oil flowing per unit time is required, which is likely to increase the scale of the equipment.
In addition to the problem in (b), the press machine slide drive apparatus in (c) described above has a non-linear characteristic from the drive axis driven by the hydraulic motor to the slide, causing an additional problem of adding constraints to the slide pressurization value, etc.
Moreover, the press machine slide drive apparatus in (d) described above has also a problem of drastically decreasing controllability of the electric motor (affected by compressibility of oil pressure and leakage of the hydraulic oil) by letting the oil pressure stand in some midpoint of the drive section. Furthermore, the press machine slide drive apparatus in (d) described above inherits the problem specific to control of an electric motor of not being provided with an energy storing function and the work-load required for press pressurization and press molding is limited by maximum instantaneous output of the electric motor. On the other hand, its advantage is limited to the ability to construct a system easily.
As shown above, for the conventional press machine slide drive apparatus, etc., a type of driving the slide by an electric (servo) motor has been designed with prime importance placed on controllability, but the magnitude of slide pressurization and energy performance are drastically decreased considering its capacity (size of the motor, output (W), power reception capacity). On the other hand, the drive (by a variable capacity pump) using a hydraulic pressure makes it possible to freely secure pressurization and energy, but nonetheless deteriorates its controllability considerably due to compression of the hydraulic oil and leakage of the hydraulic oil. These types have both advantages and disadvantages. In contrast to these types, there is also a type of driving the hydraulic pump with an electric (servo) motor, but this still includes both types of problems and cannot contribute to functional solutions.
The present invention has been achieved in view of the above-described circumstances, and has as its object the provision of a drive apparatus, press machine slide drive apparatus and method capable of combining an electric motor and a hydraulic pump/motor such as oil hydraulic pump/motor on a torque level, controlling the press machine using controllability of the electric motor and regenerating kinetic energy of the slide during braking without being constrained by slide pressurization and amount of energy (performance).
In order to attain the above-described object, the present invention is directed to a drive apparatus comprising: an electric motor, a fixed capacity type or variable capacity type hydraulic pump/motor connected to a constant high pressure source that generates a quasi-constant pressure hydraulic liquid and a low pressure source and a torque transmission device which connects a drive axis and the electric motor in such a way that torque is transmitted between drive axis and electric motor and connects the drive axis and hydraulic pump/motor in such a way that torque is transmitted between the drive axis and hydraulic pump/motor.
Furthermore, the present invention is directed to a press machine slide drive apparatus comprising: an electric motor, a fixed capacity type or variable capacity type hydraulic pump/motor connected to a constant high pressure source that generates a quasi-constant high pressure hydraulic liquid and a low pressure source, a slide drive mechanism which drives a slide of a press machine and a power transmitting device which connects a drive axis of the slide drive mechanism and the electric motor in such a way that torque is transmitted between the drive axis of slide drive mechanism and the electric motor and connects the drive axis and the hydraulic pump/motor in such a way that torque is transmitted between the drive axis and hydraulic pump/motor.
That is, according to the present application, the electric motor and hydraulic pump/motor are used together and especially the constant high pressure source that generates a quasi-constant pressure hydraulic liquid and a low pressure source are connected to the hydraulic pump/motor to thereby eliminate torque response delays of the hydraulic pump/motor, thus making it possible to realize a combination with the electric motor on a torque level, control the press machine with controllability of the electric motor and freely secure the magnitude of slide pressurization and energy.
The present invention is directed to a press machine slide drive apparatus comprising: an electric motor, a fixed capacity type or variable capacity type hydraulic pump/motor connected to a constant high pressure source that generates a quasi-constant pressure hydraulic liquid and a low pressure source, a plurality of slide drive mechanisms which drives one slide of the press machine and a power transmission device which connects each drive axis and the electric motor in the plurality of slide drive mechanisms in such a way that torque is transmitted between each drive axis and the electric motor and connects each drive axis and the hydraulic pump/motor in such a way that torque is transmitted between the each drive axis and the hydraulic pump/motor.
According to the present application, one slide is driven by drive axes of a plurality of slide drive mechanisms, and therefore it is possible, even when decentered press weight is applied to the slide, to realize torque control according to the decentered press weight and maintain the parallelism of the slide with high accuracy.
The present invention is directed to a press machine slide drive method comprising a step of driving an electric motor and generating torque, a step of generating torque from a fixed capacity type or variable capacity type hydraulic pump/motor by connecting the hydraulic pump/motor to a constant high pressure source which generates a quasi-constant high pressure hydraulic liquid and a low pressure source and a step of combining and acting the output torque of the electric motor and the output torque of the hydraulic pump/motor on the drive axis when the output torque of at least the single electric motor unit is not sufficient as the torque output to the drive axis of the press machine slide drive mechanism.
That is, when a large slide pressure is required and the output torque of the electric motor alone is not enough, this embodiment combines the output torque of the electric motor with the output torque of the hydraulic pump/motor to assist the slide in obtaining the required pressure.
The present invention is directed to a press machine slide drive method comprising a step of rendering the hydraulic pump/motor to operate as a hydraulic pump when load in one cycle of the press machine is low, a step of generating torque larger than the torque necessary during the low load from the electric motor in such a way as to balance with the low load and the load of the hydraulic pump/motor and a step of storing surplus energy caused by surplus torque of the electric motor caused by the pump operation of the hydraulic pump/motor in the constant high pressure source as a hydraulic liquid.
That is, when the press machine is operating with low load such as uniform motion, this embodiment operates the hydraulic pump/motor as the hydraulic pump and generates larger torque by an amount corresponding to the load of this hydraulic pump/motor from the electric motor than torque required for the low load operation. As a result, the pump operation of the hydraulic pump/motor causes the surplus energy accompanying the surplus torque of the electric motor to be stored (charged) in the constant high pressure source as the hydraulic liquid.
Preferably, the press machine slide drive method further comprises a step of rendering the hydraulic pump/motor to operate as a hydraulic pressure pump when the slide is decelerated in one cycle of the press machine and storing the whole or part of the kinetic energy of the slide in the constant high pressure source as a hydraulic liquid.
That is, this embodiment regenerates the kinetic energy retained by the slide into the constant high pressure source via the hydraulic pump/motor during deceleration (braking) operation of the slide and makes braking torque act on the slide as a regenerative reaction force for effective utilization of energy.